In the last part of the course we make a
review of selected technical problems in
multimedia signal processing
First problem:
CONTENT SECURITY
AND WATERMARKING
• DIGITAL CONTENT (AUDIO,
VIDEO, GRAPHICS, IMAGES)
CAN BE EASILY COPIED, TRANSMITTED
AND DISTRIBUTED
THIS HAS GREAT ADVANTAGES AND
BUSINESS POTENTIAL, NO PHYSICAL
MEDIA AND TRANSPORT IS NEEDED
EXAMPLE: Nokia Ovi store
Buying music, movies, pictures, maps from the
network means that content has to be protected
against copying
• DIGITAL MEDIA BRINGS ALSO BIG
PROBLEMS FOR CONTENT OWNERS
DUE TO UNAUTHORIZED USE. THEY CAN
EASILY LOSE THEIR PROPERTY AND
BUSINESS
• CONTENT OWNERS NEED THUS A
STRONG PROTECTION OF THEIR
CONTENT AGAINST UNAUTHORIZED
USE
• CONTENT PROTECTION IS QUITE
DIFFICULT AND INCLUDES MANY ASPECTS
THIS PROBLEM IS KNOWN CURRENTLY
UNDER THE NAME DRM
DIGITAL
RIGHTS
MANAGEMENT
• WHAT ARE THE REQUIREMENTS FOR
THE DRM?
- DRM SHOULD PREVENT AGAINST COPYING
- DRM SHOULD AUTHORIZE ACCESS
LIMITED TO: PARTICULAR USER,
SPECIFIC TIME, SPECIFIC NUMBER
USAGE AND COPIES, ETC.
- DRM SHOULD FACILITATE PAYMENT
FOR CONTENT (E.G. RENTING FOR SPECIFIC
TIME AND RENEWAL OF RIGHTS)
• ALL REQUIREMENTS FOR DRM ARE VERY
DIFFICULT TO SATISFY
• IN PARTICULAR THEY ARE DIFFICULT IF THE
DRM SYSTEM WOULD BE STANDARDIZED,
THAT IS IS STRUCTURE WOULD BE KNOWN
TO EVERYBODY
• THIS IS BECAUSE STANDARDIZED SYSTEM
MIGHT BE EASIER TO BREAK THAN SECRET
SYSTEM
• IN PRINICPLE DIGITAL CONTENT CAN
BE EASILY (?) PROTECTED BY
ENCRYPTION AND WATERMARKING
WHAT IS ENCRYPTION?
ENCRYTPION MEANS THAT THE
CONTENT BITS ARE MANIPULATED IN
SECRET WAY BY SOME ALOGRITHM.
• THE ORIGINAL BITS CAN BE RECOVERED BY
REVERSING THE OPERATION OF THE
ALGORITHM, REVERSE ALGORITHM IS
CALLED DECRYPTION SO WE HAVE TWO
ALGORITHMS WHICH CAN REVERSE:
CONTENT
ENCRYPTION
ALGORITHM
DECRYPTION
ALGORITHM
CONTENT
•
BUT SUCH SYSTEM HAS PROBLEMS
1. IF ALGORITHM IS KNOWN, EVERYBODY
WILL USE IT
2. HOW TO CONTROL THE ACCESS TO
CONTENT? WHAT IF USERS BUY ACCESS
FOR SOME TIME AND FOR SOME
CONTENT ONLY?
3. WHAT TO DO WITH USERS WHICH
WILL USE PROPER ACCESS FOR
ILLEGAL COPYING AND DISTRIBUTION
OF CONTENT?
•
•
THUS THE DRM CONTENT PROTECTION
MUST BE MORE CLEVER.
IT HAS TO BE BASED ON
1. CONDITIONAL ACCESS
2. ENCRYPTION ALGORITHMS
2. WATERMARKING
• WHAT IS CONDITIONAL ACCESS?
IT IS ACCESS GIVEN ON LIMITED
CONDITIONS, E.G. TIME, CONTENT,
PAYMENT AND SO ON
CONDITIONAL ACCESS ENABLED AFTER PAYING
CONTENT
ENCRYPTION
ALGORITHM
DECRYPTION
ALGORITHM
CONDITIONAL ACCESS CAN BE A CARD GIVEN
TO THE USER, OR A CERTIFICATE SEND VIA
INTERNET
• EXAMPLE – THE SYSTEM USED IN
DIGITAL TELEVISION FOR WATCHING
PAY PROGRAMS,
IN THIS SYSTEM CONDITIONAL ACCESS HAS A
FORM OF SUBSCRIPTION CARD, ON THE CARD
THERE IS PROCESSOR IMPLEMENTING PART
OF CA SYSTEM
ANOTHER PART IS IMPLEMENTED IN A
MODULE CALLED CAM – CONDITIONAL
ACCESS SYSTEM, THE CARD SLIDS INTO THE
CAM. THIS MODULE MAKES POSSIBLE TO USE
DIFFERENT CA ALGORITHMS BY DIFFERENT
OPERATORS
RECEIVER FOR DIGITAL TELEVISION
SUBSCRIPTION CARD
CAM MODULE
• ONE RECEIVER CAN ALSO HAVE SEVERAL
CAM’s WITH CARDS FOR RECEIVING
PAY PACKAGES FROM DIFFERENT
OPERATORS.
SUCH SYSTEMS ARE WIDELY USED IN
TELEVISION.
BUT MANY OF THE SYSTEMS WERE ALSO
BROKEN SINCE ONE CAN ANALYZE
PROGRAM ON THE CARD AND TRACE
TRAFFIC BETWEEN THE CARD AND CAM.
• ENHANCED SOLUTION:
AUTHENTICATE THE USER
THIS CAN BE DONE IF THE USER
IS CONNECTED TO THE TELEPHONE OR
THE INTERNET, THE SYSTEM CAN
CHECK IF THE ORIGINAL CARD IS USED.
• BUT WHAT TO DO IF A USER HAS
VALID SUBSCRIPTION BUT USES
IT FOR RECORDING AND DISTRIBUTING
CONTENT ILLEGALLY? IN THIS CASE
WE CAN NOT PROTECT THE CONTENT
ONE SOLUTION IS TO PREVENT
RECORDING AND/OR TO PREVENT
GETTING THE RECORDING OUT
OF THE DEVICE
• FOR EXAMPLE IN MEDIA TERMINAL USER
CAN RECORD DIGITAL TV PROGRAMS
ON INTERNAL HARD DISC
• BUT RECORDED CONTENT IS
ENCRYPTED AND THERE IS NO
WAY OF GETTING IT OUT OF THE
TERMINAL
• STILL, HACKERS MAY BE ABLE
TO BREAK SUCH SYSTEM TOO
• THUS, TO PROTECT THE CONTENT
TECHNICALLY MIGHT BE SOMETIMES
DIFFICULT OR EVEN IMPOSSIBLE
• THE ONLY WAY TO DEAL WITH IT
COULD BE MARKING THE CONTENT IN AN
INVISIBLE WAY TO DETECT WHO AND WHEN
COPIED IT.
THIS CAN BE USED AS A PROOF FOR
CRIMINAL OFFENCE AND FOR USING LEGAL
MEANS TO PROTECT THE CONTENT OWNER
• THE OVERALL PROBLEM OF DRM IS A
COMPLEX TECHNICAL AND LEGAL PROBLEM
MANY OF ITS ASPECTS ARE OUTSIDE OF
SIGNAL PROCESSING, THEY BELONG TO
COMPUTER AND NETWORK SECURITY AREA
BUT HOW TO MARK THE CONTENT IN
SECRET WAY IS A SIGNAL PROCESSING
PROBLEM
• MARKING OBJECTS IN AN INVISIBLE WAY
IS CALLED
WATERMARKING
WATERMARKING IS A WORD
COMING FROM PAPER MONEY WHICH IS
MARKED IN SUCH A WAY THAT IT IS
VISIBLE UNDER BACKLIGHT
OUR PROBLEM HERE IS
HOW TO MAKE DIGITAL WATERMARKING?
Why to use watermarks?
Because digital media have following
features making easy copyright violations:
•
•
•
•
Ease of replication
Ease of transmission and multiple use
Plasticity (easy to change format)
Equivalence of works in digital form
Digital Watermark definition
A method of embedding a copyright stamp into
an image, sound or video. The watermark is
embedded such that the quality of the host
media is not noticeably degraded to the human
eye/ear.
Uses of Watermarking
• Copyrighting embedding
• Data hiding (Steganography)
• Source/ownership verification
Requirements
•
•
•
•
•
•
•
•
•
for Good Watermarks
Imperceptible
Undeletable
Statistically Undetectable
Robust to Lossy Data Compression
Robust to Signal Manipulation and Processing
Operations
Unambiguous
Readily detectable
Unobtrusive
Innumerable
What Watermarking Allows
• Allows authors/artists to mark their work as
their own
• Allows companies to verify source/origin of
media on a website, detect
plagiarism/copyright infringement
• Allows receiver to verify authenticity of
media
Watermarking Techniques Examples
• Least-significant-bit (LSB) insertion and
noise manipulation
– Can insert a lot of data if image is simple
– Not very robust
• Discrete Cosine Transformation (DCT)
– Very robust
– Can’t insert large amounts of data
Watermarking Example
Using Least-Significant-Bit (LSB)
• Original GIF photo
(97KB)
• Photo containing
53KB of text (80KB)
Watermarking Example 2
Using Least-Significant-Bit (LSB)
• Original Photo (24KB) • Photo containing
29KB of text (29KB)
Watermarking Techniques
Examples
• Least-significant-bit (LSB) insertion and
noise manipulation
– Can insert a lot of data if image is simple
– Not very robust
• Discrete Cosine Transformation (DCT)
– Very robust
– Can’t insert large amounts of data
NEXT
FROM THE DIFFERENTIAL
PICTURE ONE CAN
EXTRACT THE
WATERMARK BUT...
• PEOPLE MAY TRY TO ATTACK
THE WATERMARK EVEN
IF THEY DO NOT KNOW HOW
IT IS DONE FOR EXAMPLE, THEY
MAY COMPRESS THE PICTURE OR
ENLARGE IT
WATERMARK SHOULD BE
ROBUST AGAINST THESE ATTEMPT
THIS IS SHOWN IN THE NEXT
EXAMPLES
RESPONSE TO MANY WATERMARKS
Watermarking Example 3
Using Discrete Cosine Transformation (DCT)
• Original JPEG photo
(32KB)
• Photo containing 1 line
copyright info (33 KB)
Video Watermarking
• DCT-Based Video Watermarking
– MPEG-based method
CONCLUSION
• PRESERVING COPYRIGHT WILL BE
MORE AND MORE IMPORTANT
• AT PRESENT THERE ARE NO
SYSTEMS WHICH WOULD BE
RESISTANT TO ALL COPYRIGHT ATTACKS
• WATERMARKS CAN BE PRODUCED BUT
THE ACTUAL METHODS ARE SECRET